Wireless networks allow wireless devices to send and/or receive wireless signals containing voice traffic, data traffic, control signals, and/or any other suitable information. FIG. 1 illustrates an example of a wireless network 100 that includes wireless devices 110a-110e (e.g., user equipment, UEs) and a plurality of radio access nodes 120a-120b (e.g., eNodeBs or base stations) connected to one or more core network nodes 130 via an interconnecting network 125. Wireless devices 110 may each be capable of communicating directly with radio access nodes 120 over a wireless interface. Wireless devices may also be capable of communicating with each other via device-to-device (D2D) communication.
Wireless device 110 may be capable of moving in and out of various coverage scenarios. At a given time, a wireless device 110 may be in one of three coverage scenarios: an In-Network Coverage scenario (INC), a Partial Network Coverage scenario (PNC), or an Out-of-Network Coverage scenario (ONC). The INC scenario is illustrated by wireless devices 110a and 110c. Wireless devices 110a and 110c are in D2D communication. Each of wireless device 110a and wireless device 110c is also within coverage of at least one radio access node 120 of the wireless network. Because each wireless device 110 is within coverage of a radio access node 120 during the INC scenario, the network can ensure that the D2D communication does not cause unnecessary interference.
The PNC scenario is illustrated by wireless device 110b. As illustrated, wireless device 110b is not capable of communicating directly with the wireless network infrastructure because it is outside the coverage area of radio access nodes 120. Wireless device 110b may be outside the coverage area due to lack of any radio access node 120 in its vicinity or due to insufficient resources in any of the radio access nodes 120 in its vicinity. In the PNC scenario, wireless device 110b is capable of communicating with wireless device 110a via D2D communication, and wireless device 110a is within coverage of a radio access node 120. Because wireless device 110a is within the coverage of a radio access node 120, wireless device 110b can communicate with the wireless network infrastructure indirectly via its D2D connection with wireless device 110a. 
The ONC scenario is illustrated by wireless devices 110d and 110e. Wireless devices 110d and 110e may each be outside the coverage area due to lack of any radio access node 120 in the vicinity or due to insufficient resources in any of the radio access nodes 120 in the vicinity. Thus, in the ONC scenario, wireless devices 110d and 110e are not communicating with the wireless network either directly or indirectly. However, wireless devices 110d and 110e may communicate with each other via D2D communication.
D2D communication can be exploited in cellular networks to improve overall network capacity as well as mitigate coverage holes for wireless devices 110 that do not have network coverage. In certain D2D communication scenarios, D2D communication may be bi-directional communication where both wireless devices 110 receive and transmit in the same or different resources. In other D2D communication scenarios, one of the wireless devices 110 transmits and the other one receives the signals. There may also exist a point-to-multipoint (e.g., multicast, broadcast) scenario in which case a plurality of wireless devices 110 receive signals from the same transmitting wireless device 110. This scenario may be particularly useful for emergency services or public safety operation to spread vital information to several wireless devices 110 in an affected area. The term D2D communication and D2D operation may be used interchangeably herein.
During D2D communication, wireless devices 110 generate radio emissions. The emissions outside of wireless device 110's frequency band are often termed as out of band (OOB) emissions or unwanted emissions. The major OOB and spurious emission requirements are typically specified by the standard bodies and eventually enforced by the regulators in different countries and regions for both wireless devices 110 and radio access nodes 120. Examples of the OOB emissions are Adjacent Channel Leakage Ratio (ACLR) and Spectrum Emission Mask (SEM). Typically these requirements ensure that the emission levels outside the transmitter channel bandwidth or operating band remain several tens of dB below transmitted signal.
To conserve wireless device 110's battery power, the power amplifier (PA) of wireless device 110 may be designed to operate efficiently. Thus, the PA may be designed for certain typical operating points or configurations or set of parameter settings, such as modulation type, number of active physical channels (e.g., resource blocks in Evolved Universal Terrestrial Radio Access (E-UTRA) or number of Code Division Multiple Access (CDMA) channelization codes code/spreading factor in UTRA). To ensure that wireless device 110 fulfills OOB/spurious requirements for all allowed uplink transmission configurations, wireless device 110 is allowed to reduce its maximum uplink transmission power in some scenarios. This is called maximum power reduction (MPR) or UE power back-off in some literature. For instance a wireless device 110 with maximum transmit power of 24 dBm power class may reduce its maximum power from 24 dBm to 23 or 22 dBm depending upon the configuration.
In E-UTRA, an Additional-MPR (A-MPR) for the wireless device 110 transmitter has also been specified in addition to the normal MPR. The A-MPR can vary between different cells, operating frequency bands, and more specifically between cells deployed in different location areas or regions. In particular, the A-MPR may be applied by wireless devices 110 in order to meet the additional emission requirements imposed by the regional regulatory organization. A-MPR is an optional feature, which may be used by the network when needed depending upon the co-existence scenario. The A-MPR defines the wireless device 110's maximum output power reduction (on top of the normal MPR) needed to fulfill certain emission requirements by accounting for factors such as: bandwidth, frequency band, or resource block allocation. The network node may control the A-MPR by signaling to wireless device 110 a parameter called network signaling (NS) parameter. For example NS_01 and NS_02 correspond to different levels of pre-defined A-MPRs.
In certain D2D scenarios, the D2D communication may be network assisted. In network assisted D2D communication, wireless devices 110 in the vicinity of each other can establish a direct radio link (D2D bearer). While wireless devices 110 communicate over the D2D “direct” bearer, they also maintain a cellular connection with their respective serving radio access node 120. This direct link is interchangeably called as network (NW) link, D2D-NW link, etc. The NW link may be used for any suitable purpose, such as resource assignment for D2D communication, maintenance of radio link quality of D2D communication link, etc. Unfortunately, known methods for network assisted D2D communication are unable to fully manage the interference. Therefore D2D communications could potentially cause interference to both serving cellular networks as well as in legacy co-located networks or co-existing networks in the same geographical region.
In LTE, potential D2D interference can be intra-frequency co-channel interference (i.e., collisions between transmitted resource blocks (RBs) within the system bandwidth) as well as interference from in-band emissions from the transmitting RBs within the system bandwidth into adjacent RBs to those RBs being employed for the desired transmission. In addition D2D communications can result in inter-device and intra-device interference across a number of channels in LTE including, such as the Physical Uplink Control Channel (PUCCH) and the Physical Uplink Shared Channel (PUSCH). The D2D communication may typically take place over LTE uplink channels such as PUCCH/PUSCH or similar channels.
As an example of inter-device interference, two wireless devices 110, X and Y, communicate via D2D communication in given subframes 2, 3 and 4 on the uplink (UL) (e.g., on UL spectrum in FDD). In these subframes, wireless device Y receives information from wireless device X in a first set of resource blocks. Also during these subframes a third wireless device Z transmits to a radio access node 120 in uplink resources in a second set of resource blocks within the same system bandwidth that wireless device Y is receiving D2D communication from wireless device X. In this example, the second set of resources is a PUCCH transmission in subframe 2 and a PUSCH transmission in subframe 3. Due to in-band emissions, wireless device Z will create a “high interference” area where wireless device Y is possibly unable to decode data from wireless device X. This “high interference” area may be a function of device Z transmit output power, the path loss to wireless device Y, wireless device C's resource block allocation, the receive power level of wireless device Y and the D2D resource block allocation, and/or wireless device C inband emission levels at the frequency of the D2D resource block allocation.
Such inter-device interference scenarios can occur in both partial (PNC) and full (INC) coverage scenarios. It is also possible that inter-device interference could occur in “no-coverage” (ONC) scenarios if, for example, wireless devices X and Y are both out of coverage, and device Z is within coverage but close to the edge of coverage and close to wireless devices X and Y, such that it can still create an exclusion zone for these devices.
D2D transmissions can be broadly classified into discovery or communications transmissions. Since PUCCH transmissions are generally pre-assigned with a fixed periodicity, the PUCCH transmissions could potentially impact both the discovery and the communications phases of D2D. However with regard to PUSCH transmissions, the PUSCH transmissions of wireless device Z could be scheduled to avoid the discovery phase of the D2D transmissions, but likely not the D2D transmissions during the communications phase. The interference zone due to the inband emissions for these inter-device scenarios can be quite large, potentially on the order of tens or hundreds of meters.
As an example of intra-device interference, such interference may occur when wireless device X is transmitting simultaneously both to a nearby wireless device Y using D2D communication in a first set of resource blocks, and transmitting to a network (NW) node using a second set of resource blocks. An example scenario for this would be when a device X transmits a beacon signal (or pilot signal) and simultaneously transmits a PUCCH to the network node, but other scenarios may also exist. Note that the intra-device interference may be limited to full (INC) and partial (PNC) coverage scenarios.